The invention relates to a reflected or transmitted light scanner and an image processing method for scanned-in image samples.
When scanning image samples, the scanned images often exhibit defects that may have various causes. A potential cause for the defective areas may be image light dispersed on scratches of the sample. Other potential causes are dust or other particles present on the sample or on the image recording device, or errors in the imaging optics or the recording device.
Several methods have already been recommended to correct these types of defects in the image.
U.S. Pat. No. 4,680,638 describes a method that uses an infrared scan for correcting defects for a video film. The defect that is detected using the infrared scan is corrected either by replacing the image information with information of a previous image of the film, or through interpolation of the defective area. However, replacing the defective image area with information from the previous image is only practical for video films, where essentially the same image is recorded multiple times. The interpolation method is also suitable for individual image scanners, however its computing time is time-consuming because each individual defective pixel needs to be considered together with its adjacent pixels.
U.S. Pat. No. 5,266,805 also describes a method for correcting defects that is based on taking an infrared signal in addition to the red, green and blue signals. The infrared signal provides information regarding the position and magnitude of the defects. This method recommends correcting minor defects—that is, defects with an infrared signal that is below a certain threshold—by dividing the image signal by the infrared signal. Stronger defects where it is no longer possible to detect color information are eliminated by interpolation. With this correction method, the computing of the interpolation is very time-consuming as well, thus preventing quick processing of the scanned-in images.
The German Patent application No. DE 100 29 826 5, recommends recording in a different spectral range in place of the infrared scan in addition to the three color scans of the image sample. This additional defect scan is then computed together with the image signals in the three colors in order to eliminate the defects. This method is very computing time intensive as well and is additionally dependent on the film type.
Computing intensive image processing methods are not practicable due to today's demands to generate as many images as possible in a short time and at an excellent quality. This is especially so in large-scale photo labs and also when using simple flatbed scanners.